AMERICAN GEOPHYSICAL UNION
WASHINGTON– Glacial melting due to global warming is likely the cause of a shift in the movement of the poles that occurred in the 1990s.
The locations of the North and South poles aren’t static, unchanging spots on our planet. The axis Earth spins around–or more specifically the surface that invisible line emerges from–is always moving due to processes scientists don’t completely understand. The way water is distributed on Earth’s surface is one factor that drives the drift.
Melting glaciers redistributed enough water to cause the direction of polar wander to turn and accelerate eastward during the mid-1990s, according to a new study in Geophysical Research Letters, AGU’s journal for high-impact, short-format reports with immediate implications spanning all Earth and space sciences.
“The faster ice melting under global warming was the most likely cause of the directional change of the polar drift in the 1990s,” said Shanshan Deng, a researcher at the Institute of Geographic Sciences and Natural Resources Research at the Chinese Academy of Sciences, the University of the Chinese Academy of Sciences and an author of the new study.
The Earth spins around an axis kind of like a top, explains Vincent Humphrey, a climate scientist at the University of Zurich who was not involved in this research. If the weight of a top is moved around, the spinning top would start to lean and wobble as its rotational axis changes. The same thing happens to the Earth as weight is shifted from one area to the other.
Researchers have been able to determine the causes of polar drifts starting from 2002 based on data from the Gravity Recovery and Climate Experiment (GRACE), a joint mission by NASA and the German Aerospace Center, launched with twin satellites that year and a follow up mission in 2018. The mission gathered information on how mass is distributed around the planet by measuring uneven changes in gravity at different points.
Previous studies released on the GRACE mission data revealed some of the reasons for later changes in direction. For example, research has determined more recent movements of the North Pole away from Canada and toward Russia to be caused by factors like molten iron in the Earth’s outer core. Other shifts were caused in part by what’s called the terrestrial water storage change, the process by which all the water on land–including frozen water in glaciers and groundwater stored under our continents–is being lost through melting and groundwater pumping.
The authors of the new study believed that this water loss on land contributed to the shifts in the polar drift in the past two decades by changing the way mass is distributed around the world. In particular, they wanted to see if it could also explain changes that occurred in the mid-1990s.
In 1995, the direction of polar drift shifted from southward to eastward. The average speed of drift from 1995 to 2020 also increased about 17 times from the average speed recorded from 1981 to 1995.
Now researchers have found a way to wind modern pole tracking analysis backward in time to learn why this drift occurred. The new research calculates the total land water loss in the 1990s before the GRACE mission started.
“The findings offer a clue for studying past climate-driven polar motion,” said Suxia Liu, a hydrologist at the Institute of Geographic Sciences and Natural Resources Research at the Chinese Academy of Sciences, the University of the Chinese Academy of Sciences and the corresponding author of the new study. “The goal of this project, funded by the Ministry of Science and Technology of China is to explore the relationship between the water and polar motion.”
Water loss and polar drift
Using data on glacier loss and estimations of ground water pumping, Liu and her colleagues calculated how the water stored on land changed. They found that the contributions of water loss from the polar regions is the main driver of polar drift, with contributions from water loss in nonpolar regions. Together, all this water loss explained the eastward change in polar drift.
“I think it brings an interesting piece of evidence to this question,” said Humphrey. “It tells you how strong this mass change is–it’s so big that it can change the axis of the Earth.”
Humphrey said the change to the Earth’s axis isn’t large enough that it would affect daily life. It could change the length of day we experience, but only by milliseconds.
The faster ice melting couldn’t entirely explain the shift, Deng said. While they didn’t analyze this specifically, she speculated that the slight gap might be due to activities involving land water storage in non-polar regions, such as unsustainable groundwater pumping for agriculture.
Humphrey said this evidence reveals how much direct human activity can have an impact on changes to the mass of water on land. Their analysis revealed large changes in water mass in areas like California, northern Texas, the region around Beijing and northern India, for example–all areas that have been pumping large amounts of groundwater for agricultural use.
“The ground water contribution is also an important one,” Humphrey said. “Here you have a local water management problem that is picked up by this type of analysis.”
Liu said the research has larger implications for our understanding of land water storage earlier in the 20th century. Researchers have 176 years of data on polar drift. By using some of the methods highlighted by her and her colleagues, it could be possible to use those changes in direction and speed to estimate how much land water was lost in past years.
###
AGU supports 130,000 enthusiasts to experts worldwide in Earth and space sciences. Through broad and inclusive partnerships, we advance discovery and solution science that accelerate knowledge and create solutions that are ethical, unbiased and respectful of communities and their values. Our programs include serving as a scholarly publisher, convening virtual and in-person events and providing career support. We live our values in everything we do, such as our net zero energy renovated building in Washington, D.C. and our Ethics and Equity Center, which fosters a diverse and inclusive geoscience community to ensure responsible conduct.
Discover more from Watts Up With That?
Subscribe to get the latest posts sent to your email.
I’m confused, it’s not EurekAlert!?Charles found a source for nonsense even more ridiculous than EurekAlert!, is that possible?
The once-revered AGU beclowns itself once again.
The butterfly effect. If man caused the change it is so small we wouldn’t notice. Good to know it is being studied.
Why would anyone take these,,,well, people, seriously?
Migrating geese are shifting the Earth’s axis as we speak….
At scale, the earth’s crust is thinner than the skin of an apple. The amount of water or ice involved is only a small fraction of the crust.
One might as well look for orbital changes due to el nino or lunar cycles.
Hush. Don’t give them any more crackpot ideas to float!
The movement of our axis of rotation is a combination of normal top-like precession, and the changes in the distribution of mass from melting ice and isostatic rebound. However, the recent changes are small compared to the historical past! See the attached graph.
The last glaciation started to wane almost 21 thousand years ago. The initial melt-water pulse from about 15,000 to 7,000 years ago was significantly greater and would have had a much greater change on the distribution of mass than what Earth has experienced in the last 7,000 years, let alone the last couple of decades. To put everything in perspective, nothing unusual with respect to melting has happened recently that can be uniquely attributed to industrialization, as evidenced by the change in sea level.
A noteworthy point is that in section 5 of the original article:
( https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020GL092114 )
they remark, “Accelerated ice melting in glacial areas cannot explain the entire polar drift in the 1990s, especially for peak‐to‐peak amplitudes.” They follow that up with, “Thus, polar motion is more sensitive to TWS [terrestrial water storage] changes in mid‐latitude areas than in other areas.” Therefore, this article is more about aquifer draw-down in agriculture, and perhaps the NASA documented greening of Earth from increased CO2, than it is about climate change or glacier melting.
After reading the actual research article, I note that there is no mention of the outer core or magnetic pole movement. The reference to the impact of molten iron in the outer core refers to the wandering of the MAGNETIC pole, which is unrelated to the drift of the GEOGRAPHIC poles! While both are driven by the Earth’s rotation, they are different effects. This is a mix of limes and oranges. It appears that whoever prepared the AGU press release felt that they knew more than the authors of the research article.
The quality of science communicated by press releases continues its decline.
Several commenters here are confusing this discussion with the movement of the magnetic poles. It seems to me that they are actually referring to the Chandler wobble, discovered in 1891:
https://en.wikipedia.org/wiki/Chandler_wobble
Clyde, I agree with your observation – the press release itself appears to make the same error of mixing magnetic pole movement with changes in rotational axis. (I had not seen your comment when I submitted mine, but thanks for the link to the actual paper.)
The IERS (/ “Observatoire de Paris”) website has the EOPC04 daily data from (1/1/)1962, projected as “X” and “Y” values in arc-seconds onto (essentially ? …) a “polar projection” grid [ something like “X = Distance (from the North Pole) along the 90°E meridian”, “Y = Distance along the 180° meridian” with each circle of latitude having a fixed radius ??? ].
The data I used was in the “C04 with Celestial Pole offsets (dX,dY) referred to IAU 2000 precession-nutation model” link (NB : a text file roughly 3.5MB in size !).
With 2 points at (X1, Y1) and (X2, Y2), the “distance” (in arc-seconds : 1 arc-minute on the Earth’s surface = 40000/(360 x 60) ~= 1.85 km, 1″ ~= 30 metres ?) between them can easily be calculated using Pythagoras.
Extracting just the data lines for the first of each month, calculating “distances” (in tenths of arc-seconds …) and plotting the results reveals a change to an “odd / distorted” behaviour regime since 2010.
Absolutely nothing around 1990 …
Forgot to include plots …
… plural …
From the above article, firstly: “. . .research has determined more recent movements of the North Pole away from Canada and toward Russia to be caused by factors like molten iron in the Earth’s outer core. Other shifts were caused in part by what’s called the terrestrial water storage change, the process by which all the water on land–including frozen water in glaciers and groundwater stored under our continents–is being lost through melting and groundwater pumping.”
Then followed by this: “They found that the contributions of water loss from the polar regions is the main driver of polar drift, with contributions from water loss in nonpolar regions. Together, all this water loss explained the eastward change in polar drift.”
Left unsaid: how the “researchers” were able to conclude that water loss from polar regions was more significant than shifting molten iron in Earth’s outer core in terms of causing polar drift.
Given the relative mass differences between these two factors, I’m betting on the molten iron shifting as the predominant cause.
Eh??
They seem to be talking about the magnetic pole. But the magnetic pole has nothing to do with the spin-axis of the Earth, which is relatively static.
And there is no way that oceanic cycles can effect the magnetic pole.
So what is this report talking about?
R
From the second paragraph of the above article:
“The locations of the North and South poles aren’t static, unchanging spots on our planet. The axis Earth spins around–or more specifically the surface that invisible line emerges from–is always moving due to processes scientists don’t completely understand.” (my bold emphasis added). As you point out, this is different from a line that connects Earth’s north and south magnetic poles.
You mention the spin-axis of Earth being “relatively static”, which indeed it is. According to the Deng, et.al. [2021] GRL research letter that was referenced, but not linked, above (which is freely available at https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2020GL092114 ),
polar motion observations show that the Earth’s spin axis drifted from January 1981 to June 2020 at a rate of about .003 seconds of arc per year. That’s relatively tiny, amounting to less than two-tenths of a degree-of-arc-change over 20 years.
Totally ignoring earthquakes? The 2010 magnitude 8.8 quake in Chile supposedly had an effect of 3 inches alone.
The mass of Volcanic lava flows in the deep trenches and other active volcanic sites, has more effect on the spinning earth than the small increase in the water levels which spread everywhere. There is also the subduction of the earths plates. As those plates are melted the molten material will be added to the molten core of the earth. It is funny how everyone blames the climate change on CO2 when these other activities are going with far greater mass. Money and politics really cloud the perspectives of these myopic scholars.
I think this is the most preposterous thing I’ve ever heard attributed to global warming, and that is really saying something.
Low indirect solar forcing driving a warm AMO phase since 1995. Real climate change, it happens every centennial solar minimum.
What about Guam? Does this make it more likely that Guam will capsize?
Now that we are able to measure something more precisely, we are able to detect smaller changes in that thing?
Isn’t that typically the case?
It’s Stupid. That’s AGU!
Even if some gigatonnes (10^12 kg each) of ice were to melt and flow into the sea, that would only shift less than one part per trillion of the earth’s mass (about 6 x 10^24 kg). If the axis of rotation of the earth was changed, even by less than a second of arc, this would require a huge change in the angular momentum of the earth. A change in angular momentum requires a torque–where would this torque come from?
But, if we believe one of our genius Congressmen, if all the soldiers stood on one side of Guam, it might tip over.
But won’t that depend on how water distributes in oceans – ‘sloshing’ in the South Pacific-Indian ocean area for example, varying in year terms not decades? Winds being a factor.
Note the amount of melt is small, and some glaciers are growing.
Do volcanoes have much effect? Some spew huge amounts of ash, though breadth of distribution varies. (Mt. St. Helens ash drifted as far as Winnipeg MB, though largest depth of deposition was closer such as in Spokane WA (IIRC at least a quarter inch whereas Calgary AB was only a sixteenth). And mud went way downstream to the west. I don’t have perspective on how much mass that was. (That eruption blew the side off the mountain, IIRC mud resulted from the snow on its peak.) I suppose molten material, as common in Hawaii for example, does not travel far (there and especially from an underwater volcano the water quenches it soon).
Just for the record, I predicted two to three years ago they were going to be making that claim on this very website
The authors are writing about the projection of the earth’s axis of rotation on the surface of the earth and the subsequent average annual movement of that point (Polar Motion) against a reference point established in 1900. Both the US Naval Observatory and the IERS track this movement and have been publishing data have published data tables going back to about 1890.
The authors make it sound like there was little or no polar motion movement relative to the earth’s crust before AGW, then suddenly the poles moved 4 meters because of AGW. Polar motion relative to the earth’s crust has been measured since at least 1900 and occurs at an average rate of 0.10 m per year. There are also higher frequency wobbles, the Chandler wobble (9 meters per 433 days) and other nutations (higher frequency excitations that diminish with time) which must be removed from the annual positional time series to get an average annular polar shift.
SO if we look at the annual average movement of the axis of rotation of the poles since 1900 what do we see?
From McCarthy et al, 1996:
“Historical sources of polar motion (1900-1990) are analyzed together with modern data in order to compile a set of coordinates of the mean pole in a reference system consistent with that of the International Earth Rotation Service. The trend and quasi‐periodic motion of the pole are investigated, and we find that the rotational pole appears to be moving at the rate of 0.333 arcsec century−1.”
An arcsec converts to about 98 feet on the earth’s surface, then .333 arcsec per century equals about 32.6 feet per century or about 10 meters per century or about 1 meter per decade.
If you look at plots of the polar position over time 1900-1990 (see US Naval Observatory, GJI 125, 623-629) you will find that annual Polar Motion can be close to zero (or even negative) in some years or as much as 25 cm (~8 mas) in other years. The accuracy of the 1900-1980 optical measurements were +/- 6 cm in any one year (Robertson and Carter 1985) relative to the original reference point and the measurement errors therefore are not cumulative. After AGW, according to the article, the pole moved about 4 meters in 40 years, or at an average rate of 0.1 meter per year, so I see little or no deviation in the average velocity of Polar Motion over the past century using the complete time series. They use a small subset of the years to calculate their claimed acceleration (1982-95). Why did they not use the 1900-2000 average of 0.1 m per year (based on 10 meters +/- 0.06 meters per 100 years)? I suspect because it did not indicate a significant deviation.
Clearly, as the authors state, the direction of movement appears to have changed around 1995-2005 (but probably about 2005-see also Chen et al 2013 Fig 2) and the authors propose it was caused by AGW. We know other natural events cause changes in the rate and direction of Polar Motion, some are internal to the earth’s mantle, some are due to surface changes in water or ice distribution and some are caused by episodic events (earthquakes and meteor impacts).
So that leads us to an important question:
Does the plot of Polar Motion since 1900 show other similar directional deviations pre AGW? And the answer is yes, (see US Naval Observatory, GJI 125, 623-629). In the period 1931-1949 there was a 70 mas (+/- 2 mas) change to the east about the same as we see from 2000-2012 (as seen in Chen et al 2013).
So the deviation described in the article appears within the historical (since 1900) natural variation of the polar rotation position changes seen pre-AGW. Current workers discard these earlier estimates of polar motion because they were measured with optical instruments and not measured with the more sophisticated modern laser range finding equipment and GPS geodesy in use since 1980. The accuracy of the satellite measurements is reported to be +/-1mm, the optical devices +/-60 mm.
In conclusion, based on published data, the RATE of polar position movement (Polar Motion) has not changed significantly when compared to the 1900-2000 average. The direction of movement changed in 2000-2005 but has historical precedent before AGW. Similar changes occurred in 1931-1949, 1910-1917 and 1964-1975. If natural forces other than AGW have caused similar directional deviations in the past how can we be certain this deviation was not caused by natural forces other than AGW?